Determining Module Inter-Row Spacing
In this article you will earn how to calculate the inter-row spacing for tilted or ground mounted PV systems. You may avoid potential shading issues and have the ability to increase the system size.
When designing a PV system that is tilted or ground mounted, determining the appropriate spacing between each row can be troublesome or a downright migraine in the making. However, it is important to do it right the first time to avoid accidental shading from the modules that are ahead of each row. This can lead to under-performing systems and angry customers. No one wants to have that. The same can be said about overcompensation too. Think of how many more kW’s you could have had. This article will get you started off on the right foot with a simple and fast process to get you out in the field faster with great results.
The first step in calculating the inter-row spacing for your modules is to calculate the height difference from the back of the module to the surface. To do that, follow this calculation below:
Height Difference = Sin (Tilt Angle) x Module Width
***Make sure you’re calculating in degrees, not radians***
In this case, I am using a SolarWorld module that has a width of 39.41 inches at a tilt angle of 15º.
Height Difference = Sin (15) x 39.41
Height Difference = 10.2” rounded down to 10”
To calculate the Module Row Spacing we need to hop over to http://solardat.uoregon.edu/SunChartProgram.php to determine what our Sun Elevation Angle is going to be. You will enter in your site's zip code or be more precise you should enter the latitude and longitude of the location for more accurate results.
When you get your results it will look something like this:
In this example, I picked a 9 AM to 3 PM window during the winter solstice for the worst case scenario. You may opt for a less stringent case to suit your needs. I chose this example because some utilities require the 9am-3pm window when offering rebates for customer owned PV systems.
From the chart, you see that I have highlighted this window and drawn a horizontal line out to the left of the chart to narrow in on the Solar Elevation Angle at those times. I estimate a 17º angle which I will use next to determine the Module Row Spacing using the formula below.
- Module Row Spacing = Height Difference / Tan (17)
- Module Row Spacing = 10 / Tan (17)
- Module Row Spacing = 32.7” rounded up to 33”
There you have it! The inter-row spacing between the trailing edge of the first row of modules and the leading edge of the next row needs to be 33”
We’re not done just yet and you’ll be glad you kept reading along…
The next thing we must do is account for the Azimuth angle and use that figure to apply that to another formula. Take a look again at the example below; you’ll see that I have drawn two vertical reference lines down from each time reference. The difference between South going in either direction turns out to be 44º and we will use this in the following formula to determine the Minimum Module Row Spacing!
- Minimum Module Row Spacing = Module Row Spacing x Cos (Azimuth Correction Angle)
- Minimum Module Row Spacing = 33 x Cos (44)
- Minimum Module Row Spacing = 23.7” rounded up to 24”
Hey, you just gained an extra 9” for every row you have in your system! On cramped roofs or large commercial systems that can make all the difference. Put another way, in this scenario we could potentially increase the system size by 27%! What do you think about that?
And one last thing….
This last calculation is just a bonus and can help you layout your array in CAD a bit easier. The following formula gives you the distance from the trailing edge of one row to the trailing edge of the subsequent row or your Row Width.
- Row Width = Minimum Module Row Spacing + Cos (Tilt Angle) x Module Width
- Row Width = 24 + Cos (15) x 39.41
- Row Width = 62”
Now go break out the TI-86 and put in some fresh batteries, I think you’ll enjoy figuring out the inter-row spacing for all of your tilted or ground-mounted PV systems. Have fun!
Could you make a couple of plug-in formulas for this calculation?
Hello. We don't typically send plug-in formulas within web pages, but the article does present some obvious formulas that you can apply to your particular application. That being said if you need engineering support, we are very glad to help address any issues you may have. Just let me know. Thanks again.
Good write up, Does this equation for determining row width hold good for single axis tracked panel rows which run north south.
The panels in each row tilt maximum +55/-55 towards the sun at sunrise and sunset.
Applying this height difference becomes 32.28 =32, module spacing =105, minimum module spacing =75
applying this in the last equation the row width comes to 97.6, is this correct or am I missing something when considering single axis tracking.
Regarding my earlier comment on single axis tracker, I realised that the azimuth correction will not apply if the location is close to the equator, please advise
Hello. Thank you for your questions. Here are our thoughts: Height Difference = 32.28”, Module Row Spacing = 105.59”, Minimum Row Spacing = 75.96”, and Trailing Edge Spacing 98.56”. This is the correct way to review ground mount layouts even for single-axis trackers when accounting for maximum tilt angles as this comment suggests. This response may or may not provide you all the information that you need. Happy to connect you with a Sales Person and/or Engineering support if you need more information. Please just contact us and provide more information on how we can support you. Thanks.
Do I need to consider azimuth correction if the solar panels are facing South direction. i.e 180deg. ? I guess azimuth correction is needed only if the panels are not facing south (considering location in India)?
This formula is based on facing due south. If not facing due south you’ll add a complex angle and slightly different width measurement that requires a bit more consideration for row spacing.
Please contact us and provide more information on how we can support you. Thanks.
Location : Robinvale, Victoria, Australia
Tilt Angle : 20 degree facing North
Panel dimension : 2015* 1000* 35 mm
Panel will be placed in portrait mode so based on this equation module width will be 2015 mm.
What will be the best and optimum inter row spacing ( Minimum to avoid shading issue)
Thank you for your comment. Calculating optimum inter-row spacing is explained in this article. I hope that it answers your questions but if you have additional specific questions please let us know and we can work to assist you. Thanks again.
Thanks so much for this write-up, it has been extremely useful.
One thing I might need help with: I have mapped all the calculations in Excel and transformed them into a dynamic graph. Everything works wonderfully, however, as soon as I include the 'Azimuth correction angle', the sun does not fully reach the 2nd row of panels. Any advice you could give?
Good afternoon. Its really hard to decipher what the issue is with your calculations/graph. One thought is that the article mentions, "Make sure you’re calculating in degrees, not radians" Hope that is helpful. Feel free to reach out to our contact us page and we can connect you to a design professional so they can talk to more about the issue. Thanks again.
I have calculated values as exactly the same as it is mentioned above because my sun chart is almost the same. My question is how did you predict the solar elevation angle 17 degree and azimuth correction angle 44 degree because one degree change has a huge impact on the final value. How to divide intervals correctly?
The Solar Elevation Angle and Azimuth Correction angle in our example are the products of selecting “a 9 AM to 3 PM window during the winter solstice for the worst-case scenario”. Once you’ve selected the window you’ll find the Solar Elevation angle by drawing the line to the corresponding angle on the Solar Elevation axis. The Azimuth Correction angle is calculated by finding the difference of 180 and the corresponding azimuth from the point you have selected in your window by drawing a line to the Solar Azimuth axis(per the example 180-136=44 & 224-180=44). As the article states you may opt for a less stringent case depending on their needs. Thank you for your question and let us know if you need additional help or you need an engineer to further assist on this project. Thanks again.